Self-drilling anchor

ABSTRACT

A self-drilling anchor installable in a wall by means of a screwdriver, the anchor being adapted to receive a threaded fastener serving to hold a fixture against the wall. The anchor includes an externally-threaded shank section having a head engageable by the screwdriver and a longitudinal bore threadably to receive the fastener. Integral with the shank section and extending axially therefrom is a drill section having at least one cutting member and guide means therefor, whereby as the anchor is turned in to the wall by a screwdriver, the cutting member then bores a round hole therein whose bank is engaged by the guide means to ensure circularity of the hole. And as the anchor continues to turn, the shank section enters and taps the hole until its head engages the outer surface of the wall to complete the anchor installation.

RELATED APPLICATIONS

This application is a division of my application Ser. No. 08/075,375,filed Jun. 4, 1993, entitled "Improved Self-Drilling Anchor", whichapplication (now U.S. Pat. No. 5,482,418), is a Division of Ser. No.08/707,661, filed May 30, 1991, (now U.S. Pat. No. 5,234,299), entitled"Improved Self-Drilling Wall Anchor" which is a continuation-in-part ofSer. No. 07/396,109, filed Aug. 21, 1989, (now U.S. Pat. No. 5,039,262),entitled "Self-Drilling Wall Anchor" which is a continuation-in-part ofSer. No. 07/215,307, filed Jul. 5, 1988 (now U.S. Pat. No. 4,892,429),entitled "Roof Anchor and Stress Plate Assembly" which is acontinuation-in-part of Ser. No. 07/081,016, filed Aug. 3, 1987 (nowU.S. Pat. No. 4,763,456), entitled "Roof anchor and Stress PlateAssembly."

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates generally to an anchor which when installed in ahole drilled in a wall is adapted to receive a threaded fastener thatserves to hold a fixture or other object against the wall, and moreparticularly to a self-drilling anchor of this type which dispenses withthe need for any tool other than a screwdriver to install the anchor andwhich is usable with fasteners of different length.

2. Status of the Prior Art

In order to mount brackets, fixtures and other objects provided withmounting holes against the outer surface of a wall formed ofplasterboard, sheetrock, fiberboard or any other material employed inhollow wall construction, the common practice is to use a hollow anchorfor this purpose. The conventional hollow anchor formed of metal orplastic, when hammered into and wedged within a hole pre-drilled in thewall, is then adapted to receive a threaded fastener or mounting screwthat goes through the mounting hole in the fixture and turns into thehollow of the anchor.

The required length of the mounting screw depends on the thickness ofthe fixture or object to be supported against the wall. Thus if theobject is a thin metal bracket, a screw of smaller length is requiredthan if the object is a thick plate or board, for this dictates a longerscrew.

The installation of a conventional anchor entails three distinctoperations, the first and most critical step being drilling a hole inthe wall, for the diameter of this hole must be appropriate to that ofthe anchor. Should an oversize hole be drilled, then in the next stepwhen the anchor is hammered into the hole, the anchor will not wedgefirmly therein but will be somewhat loose. As a consequence, it will notbe possible to carry out the third step.

In the third step, one must turn a threaded fastener into the hollow ofthe anchor, and in doing so tap the anchor. But if the anchor issomewhat loose in the wall hole, this will cause the anchor to turn asthe fastener is turned, and the fastener will therefore not be able tothread its way into the anchor.

There is also a possible fourth step that must be taken into account;for should a need arise to remove an object mounted on the wall orreplace it with another object, then one must first unscrew the fastenerfrom the anchor lodged in the wall. However, if when an unscrewingtorque is applied to the fastener, this torque causes the anchor as wellas the fastener to turn, then it will not be possible to withdraw thefastener from the anchor. The need therefore exists for an anchor which,after being lodged in a hole drilled in the wall, will resist beingturned counterclockwise and thereby make it possible to unscrew athreaded fastener from the installed anchor.

The installation of a conventional hollow anchor requires three tools: adrill provided with a drill bit having a diameter appropriate to that ofthe anchor; a hammer to drive the anchor in the hole drilled in thewall; and a screwdriver to turn the threaded fastener into the anchor orto later remove it from the anchor.

Though a typical householder or other non-professional possesses ahammer and a screwdriver, he may lack a drill. But even if he has adrill, he may not have a drill bit of the appropriate diameter for theanchor to be installed. Yet there are distinct advantages to be gainedby using hollow wall anchors to mount objects against a wall, ratherthan screws, nails or other fasteners which require no drilling butwhich have relatively poor holding power, particularly in walls made offriable materials. Nevertheless, the need for drilling has to asignificant degree heretofore discouraged the use of hollow anchors bynon-professionals.

Though hollow wall anchors are used on a large scale by professionalinstallers, the need to drill holes and then hammer the anchors intoholes is a practical drawback, for these operations are time consumingand hence impose distinct limits on the number of anchors that can beinstalled in a given period. And if anchors of different sizes must beinstalled, then the installer must change the drill bit when switchingfrom one anchor size to another, and this, too, consumes time andreduces the productivity of the installer.

To overcome these drawbacks, the 1986 patent to Ernst et al., U.S. Pat.No. 4,601,625, discloses an anchor for drywall that has anexternally-threaded cylindrical section adapted to receive a fastener,and an unthreaded drilling section. This anchor is installable usingonly a hand-powered screwdriver for this purpose, thereby dispensingwith the need for a drill and a hammer. At the upper end of the anchoris a low profile flange or head which allows the anchor to be installedflush with the drywall surface.

The Ernst et al. patent discloses an embodiment or an anchor molded ofzinc, and another embodiment formed of plastic material. Bothembodiments include a drill section that can be deflected laterally uponinsertion of a mounting screw therethrough. This makes it possible touse a single mounting screw or fastener of moderate length inconjunction with the anchor for attaching objects of various thicknessesto the wall. It is also possible when the need arises to do so, to uselonger fasteners.

In Ernst et al., the drill section is formed by a single flat bladewhose free end is notched to define a central spike and a pair ofperipheral spikes on either side of the central spike the function ofthe central spike, which extends beyond the peripheral spikes andtherefore is the first to penetrate the surface of the drywall, is tomaintain the location of the rotating drill section as a hole is drilledby the peripheral spikes. In practice, when a single blade is used tobore a hole in friable material such as drywall, the resultant drilledhole may not be perfectly round, for when this material encounters thecentral or guide spike, it tends to make the blade whip, as aconsequence of which the drilling is shifted off center and the boredhole is oversize or elliptical.

My above-identified copending application entitled "Self-Drilling WallAnchor" also discloses an anchor having an externally-threaded shanksection that terminates in a drilling section having a guide tip. Incontradistinction to the cylindrical, externally-threaded section inErnst et al., the shank section of my anchor has a root which taperstoward the drill section and a threading surrounding the root formed bya series of convolutions whose crests are of essentially the samediameter along substantially the full length of the shank section. Theadvantage of this arrangement is that as the anchor is screwed into awall of friable material, the pulverized material is then packed by thethreading into a relatively dense mass which surrounds the shank toenhance its resistance to withdrawal from the wall.

And while the self-drilling anchor disclosed in my copending applicationalso has a flange-like head of low profile similar to that of Ernst etal. so that the installed anchor will lie flush against the surface ofthe wall, in both cases these self-drilling anchors when installed bybeing turned into a wall do not offer adequate resistance to beingturned out. Yet resistance to being turned may be necessary; for when anoccasion arises requiring withdrawal of the mounting screw or fastenerfrom the anchor, in turning out the fastener with a screwdriver, thisaction will also cause the anchor to turn out; hence the fastener cannotbe withdrawn from the anchor.

SUMMARY OF INVENTION

In view of the foregoing, the main object of this invention is toprovide an improved self-drilling anchor which is installable in a wallby means of a screwdriver, the anchor being adapted to receive athreaded fastener that serves to hold a fixture or other object againstthe wall, the anchor dispensing with the need for a drill, a hammer, orany tool other than a screwdriver to install the anchor.

More particularly an object of this invention is to provide an anchor ofthe above type having an externally-threaded shank section and a drillsection extending therefrom, which when the anchor is turned into thewall, the drill section drills a round hole in the wall which is thentapped by the threading of the shank section.

A significant feature of the invention resides in a threaded anchorhaving a drill section with multiple cutting blades in which eachcutting blade is associated with a guide blade to ensure that as thedrill section is turned into the wall, the blades proceed to bore a holdwhich has a circular cross section and is not off-round or elliptical,thereby ensuring proper thread formation and maximum holding strengthwhen the shank section of the anchor taps the hole.

Another feature of the invention resides in a shank section having ahead which when the anchor is installed is pressed against the surfaceof the wall and is provided with gripping teeth that resist turning outof the anchor. Hence when it is necessary to unscrew the threadedfastener from the anchor, this action will not also cause the anchor tounscrew from the wall and thereby prevent withdrawal of the fastenertherefrom.

Also an object of the invention is to provide an anchor of the abovetype whose drill section, when forcibly engaged by the tip of thethreaded fastener as it is being advanced through the shank section, iscaused to split open to permit further advance of the fastener, wherebythe length of the fastener used may greatly exceed that of the shanksection.

A further object of this invention is to provide a self-drilling anchorhaving a drill section extending axially from an externally-threadedshank section, the drill section being in the form of a cylindrical coredrill whose bore is aligned with the bore of the shank section wherebyan elongated fastener can pass beyond the shank section and into andbeyond the drill section.

Yet another object of this invention is to provide an anchor of theabove type whose shank section has a tapered root having convolutedthreading thereon whose crests are of essentially the same diameteralong substantiality the full length of the shank section, whereby asthe anchor is turned into a wall of friable material, the resultantparticles are then packed by the threading into a relatively dense masswhich surrounds the shank to enhance its resistance to withdrawal fromthe wall.

Still another object of the invention is to provide a plastic anchorwhich is fabricated of high strength material and which can bemanufactured at relatively low cost.

Briefly stated, these objects are attained in a self-drilling anchorinstallable in a wall by means of a screwdriver or similar tool, theanchor being adapted to receive a threaded fastener that serves to holda fixture or other object against the wall. In one embodiment of theinvention, the anchor includes an externally-threaded shank sectionhaving an enlarged head that is engageable by the tool. Extending fromthe lower end of the shank section is a drill section that in oneembodiment of the invention is formed by at least one cutting blade andguide means which are so placed that as the anchor is turned into thewall by the screwdriver, the cutting blade then drills a hole whose wallis engaged by the guide means to ensure circularity of the hole. And asthe anchor continues to turn, the shank section then enters the holewhich is tapped by the threading of this section until the head engagesthe outer surface of the wall to complete the installation.

In another embodiment of the invention, the drill section is a coredrill whose bit is constituted by one or more cutting teeth, thecylindrical outer surface of the drill acting as guide means to ensurethe circularity of the drilled hole.

BRIEF DESCRIPTION OF DRAWINGS

For a better understanding of the invention as well as other objects andfurther features thereof, reference is made to the following detaileddescription to be read in conjunction with the accompanying drawings,wherein:

FIG. 1 is a perspective view of a self-drilling anchor in accordancewith the invention;

FIG. 2 is a top view of the anchor;

FIG. 3 is a magnified perspective view of the point portion of the drillsection of the anchor;

FIG. 4 is a transverse section taken through the drill section of theanchor to show the relationship of the cutting blades to the guideblades;

FIG. 5 illustrates the anchor installed in a hollow wall, a threadedfastener being received in the anchor having a length such that itextends the full length of the shank section, but not beyond;

FIG. 6 shows the installed anchor with a fastener whose length is suchas to split open the drill section;

FIG. 7 is the same as FIG. 6 except that in this instance, the fasteneracts to break off the drill section;

FIG. 8 shows the anchor with the same fastener as in FIG. 6 in which itsplits open the drill section, this anchor being installed in a doublewall;

FIG. 9 is a perspective view of a self-drilling anchor having a coredrill section in accordance with the invention;

FIG. 10 is an elevational view of the anchor;

FIG. 11 is a longitudinal section taken through the anchor;

FIG. 12 is a transverse section taken in the plane indicated by line12--12 in FIG. 11;

FIG. 13 shows the points of the drill section in relation to the hole tobe drilled; and

FIG. 14 shows the anchor installed in a hollow wall, with a threadedfastener being received in the anchor whose length is such that itextends beyond the anchor.

DETAILED DESCRIPTION OF INVENTION

The Basic Anchor:

Referring now to FIGS. 1 to 4, there is illustrated in these figures aself-drillng anchor in accordance with the invention, the anchor beingmolded of synthetic plastic material and having a hollow shank section10 and a drill section 11 integral therewith.

The synthetic plastic material from which the anchor is molded must beof high strength, and when formed to create a sharp edge, this edge mustbe capable of cutting the material of the hollow wall in which theanchor is installed. The wall is made of plasterboard, sheet rock,fiberboard and any other material used in hollow wall construction. Thismaterial is usually friable; that is to say, it is easily crumbled, andthe anchor for this wall must take this into account.

Preferably, the anchor is molded of nylon reinforced with long glassfibers (about 30% by weight) to provide a composite which is ductile andtherefore moldable at low cost. The fiberglass constituent of thecomposite affords the strength and rigidity required of the anchor andalso effective cutting edges for the drill section. In practice, thecomposite material possesses a natural or neutral color that will blendwith the surface color of the hollow wall.

Hollow shank section 10 is adapted to receive an externally-threadedfastener or mounting screw to hold a bracket, a fixture, a board of anyother object having a mounting hole against the surface of the wall inwhich the anchor is installed. The length of the fastener is appropriateto the thickness of the object to be held.

Shank section 10 has at its upper end an enlarged head 12 or flange in alow-profile, truncated conical formation. When the anchor is installedin a hollow wall of plasterboard of other relatively soft material, head12 will then sink into the wall and lie flush against its surface.

Formed on the underside of head 12 is a radial array of ratchet teeth Twhose triangular geometry is such that when the anchor is turnedclockwise into a wall and the teeth engage its surface, the teeth slipin this direction and do not impede turning, whereas should onethereafter seek to turn out the anchor, the teeth will bite into thewall to resist counterclockwise movement of the anchor. Because of thisfeature, should the occasion arise when one wishes to unscrew thethreaded fastener from an anchor installed in a wall, this action willnot at the same time cause the anchor to unscrew from the wall andthereby render it difficult if not impossible to remove the fastenerfrom the anchor.

Because the flange or head 15 is formed of composite nylon materialhaving some degree of flexure, the teeth T on the underside of the headwill yield and not cut away the plasterboard or other wall material asthe anchor is being screwed into its final position.

An advantage of an anchor whose head lies flush against the wall inwhich the anchor is installed, apart from the fact that this head doesnot slightly space the fixture or other object being mounted from thewall, is that if the fixture is later removed from the wall, and onewishes to erase the presence of the anchor, there is no need to removethe anchor. One has only to spackle over the head to provide a cleanwall surface.

Shank section 10 has a longitudinal cavity 13 therein having a cruciformformation defining at 90° intervals ridges R extending the length of theshank section. Ridges R which surround the central zone of the cavityare capable of being tapped by the threading of a metal mounting screwor fastener. One may therefore employ in conjunction with the anchormounting screws in a limited range of diameters rather than a screwhaving a predetermined diameter. And as will later be explained, themounting screw may be much longer than the length of shank section 10,for the drill section yields to permit the screw to more or less extendbeyond the shank section to accommodate fixtures or other objects ofvarious thicknesses to be mounted against the wall.

The cruciform formation of the cavity creates a socket in head 15 ofshank section 10 adapted to receive the blade of a Phillips-typescrewdriver or of a conventional screwdriver which is either manuallydriven or motor powered.

Shank section 10 has a root 14 which is tapered, whereas theconvolutions of the spiral threading 15 which surrounds the root havecrests that are of essentially the same diameter for the full length ofthe section except for the final convolution 15F which is of reduceddiameter to merge with drill section 11 and thereby avoid an abrupttransition from drill section 11 to shank section 10.

The relationship of the threading to the root is such as to causematerial which is easily pulverized as the shank section is turned intothe wall, to form a densified mass surrounding this section to resistwithdrawal of the anchor from the wall.

Drill section 11 is provided with a pair of cutting blades 16A and 16Bwhich, as best seen in FIG. 4, extend in opposite directions from thelongitudinal axis X of the anchor so that the planar cutting edges E ofthese blades are diametrically opposed and act to cut a hole H in thewall when the anchor is turned. At right angles to the respectivecutting blades is a pair of guide blades 17A and 17B which engage thebank of hole H to ensure circularity of the hole bored in the wallwhereby axis X of the anchor is colinear with the center axis of thehole.

The outer ends O_(e) of the guide blades are convex to conform to thecurvature of the bank of the hole and to sweep the bank as the drillsection is turned. In this way, a round hole is bored into the wall,thereby avoiding the tendency of a drill section having a single bladeas in the Ernst et al. patent, to cut an oversize or elliptical hole.

The lower ends of the cutting and guide blades 16A, 16B and 17A, 17B arechamfered. The lower ends of the cutting blades which are somewhatlonger than the guide blades define a triangular point P. Thus when theanchor is pressed into the surface of a wall, point P penetrates intothe surface. When the anchor is then turned by a torque-producing tool,a hole is bored therein by the cutting blades as guided by the guideblades to ensure the formation of a round hole.

In practice, the self-drilling anchor shown in FIGS. 1 to 4, instead ofbeing made of synthetic plastic material, may be fabricated of acorrosion-resistant metal such as zinc or brass.

Installation:

Referring now to FIG. 5, there is shown an anchor in accordance with theinvention installed in a hollow wall 18 whose thickness is less than thelength of shank section 10 of the anchor, so that a portion of thissection extends beyond the inner surface of the wall. It will be seenthat low-profile head 15 of the anchor lies flush with the outer surfaceof the wall and that the teeth T on the undersurface of head 15 areembedded in the wall material to resist turning out of the anchor.

Received in the hollow of shank section 10 is a mounting screw 19 whichholds a fixture 20 against the surface of the wall, fixture 20 having amounting hole 21 to admit the screw. The length of mounting screw 19 issuch that its tip is received in a conical well 22 at the lower end ofthe cavity in hollow shank section 10 just above the drill section. Inpractice, the cavity may be internally-threaded to receive the mountingscrew or it may be unthreaded so that as the mounting screw is turnedinto the cavity, it taps it way therethrough.

Because mounting screw 19 fits into the cavity of the shank section anddoes not, when fully turned in, go beyond this section, the integrity ofdrill section 11 is maintained in the arrangement shown in FIG. 5.

However, in the anchor installation shown in FIG. 6, use is made of amuch longer mounting screw 23 which when turned into shank section 10forces its way beyond the well at the lower end of the cavity and indoing so splits open drill section 11 to permit the mounting screw toexit from the shank section. Since the drill section has already carriedout its drilling function, the disruption of the drill section afterdrilling is performed does not interfere with the installation of theanchor. And since the split drill section is outside of the wall, itdoes not affect the holding power of the anchor.

It is to be noted that no notch or indentation is required in the anchorto facilitate the exit of the mounting screw from the shank section, forthe tip of the advancing mounting screw enters the conical well in theshank section cavity and then strikes the drill section at its center toeffect a splitting action in which the two cutting blades and theirassociated guide blades assume a V formation.

In the anchor shown in FIG. 7, when mounting screw 23 is turned intoshank section 10, drill section 11, instead of being split as in FIG. 6,is broken off or laterally displaced from the shank section. Tofacilitate this action, the anchor need not be provided with annulargrooves or notches at the junction of the shank and drill sections, forthe natural weakness of this junction causes the drill section to breakoff when a force is applied to this junction by the advancing mountingscrew, thereby permitting the mounting screw to exit from the shanksection. In practice, the strength of the bridge between the cuttingblades of the drill section will determine when this section will spitopen and triangulate or break off.

In FIG. 8, the anchor is installed in a double wall formed by wall 18superposed on a wall 18' of the same thickness. Hence in this instance,shank section 10, when the anchor is installed, does not extend beyondthe hollow wall but is fully embedded therein. As a consequence, whendrill section 10 is split open into a V formation, the apex portion ofthe V is lodged in wall 18' and the wings of the V act as a toggle toresist withdrawal of the anchor from the walls. Thus in a double-wallinstallation which is often used in a high quality commercialconstruction, an anchor in accordance with the invention affordsenhanced holding power.

Core Drill Anchor:

Referring now to FIGS. 9 to 12, there is shown a reusable self-drillinganchor in accordance with the invention, generally designated by numeral24, which may be molded of synthetic plastic material, such as Nylon, orof corrosion-resistant metal, such as zinc. The anchor includes a hollowshank section 25 having at its upper end an enlarged head 26 or flangein a low-profile, truncated conical formation. When the anchor isinstalled in a hollow wall of plasterboard or other relatively softmaterial, head 26 will then sink into the wall and lie flush against itsouter surface.

Formed on the undersurface of head 26 is a radial array of teeth 27,preferably in a triangular ratchet formation, so that when the anchor isturned clockwise into the wall and the teeth then engage its surface,the teeth will slip in this direction and hence not impede turning. Butshould one thereafter seek to turn out the anchor, such counterclockwisemotion will be resisted by the teeth.

Shank section 25 has a longitudinal bore 28 therein having a cruciformformation defining at 90° intervals ribs or ridges 28R extending thelength of the shank section. Ridges 28R which surround the central zoneof bore 28 are capable of being tapped by the threading of a metalmounting screw or fastener. One may therefore employ in conjunction withthis anchor, mounting screws in a limited range of diameters rather thana screw having a predetermined diameter.

The cruciform formation of the bore creates a socket in head 26 of shanksection 25 adapted to receive the blade of a Phillips-type screwdriveror that of a conventional screwdriver which is either manually driven ormotor powered.

Shank section 25 has a root 29 which is tapered, whereas theconvolutions of the spiral threading 30 which surrounds the root havecrests that are of essentially the same diameter for the full length ofthe section except for the final convolution, which is of reduceddiameter.

As pointed out in connection with the other embodiments of the anchor,the relationship of the threading to the root is such as to cause wallmaterial which is easily pulverized as the shank section is turned intothe wall, to form a densified mass surrounding this section to resistwithdrawal of the anchor from the wall.

Integral with and extending axially from shank section 25 is acylindrical core drill section 31 whose external diameter matches theexternal diameter of the tapered root 29 of the shank section at thelowermost end of this root. Hence the root of the shank section flowsinto the drill section without any discontinuity therebetween. Thelongitudinal bore 32 of the drill section is aligned with thelongitudinal bore 28 of the shank section.

The diameter of bore 32 is such as to accommodate any mounting screw orthreaded fastener capable of tapping the bore 28 of the shank section.As pointed out above, one does not have to employ with this anchor afastener of predetermined diameter, for it is usable with fasteners in alimited range of diameters, as long as the diameter of the fastener issuch that it can pass through the bore without causing the anchor toexpand, rupture or deflect.

A conventional core drill is a hollow drill that removes a cylindricalcore from the drill hole, the core drill having a cylindrical bit thatfunctions as the cutting element of the drill.

In the core drill section 31 in accordance with the invention, the bittherefor is constituted by a pair of diametrically-opposed cutting teethT₁ and T₂. Each tooth is defined by a curved wall having a triangularform. The inclined edges of the triangle function as cutting blades andthe apex as a sharp spike or point.

Hence when, as shown in FIG. 13, the anchor is pressed into a typicalwall of relatively soft material, the points P₁ and P₂ of the core drillsection penetrate the wall, the points being at the poles of thediameter D of the hole H to be drilled. This diameter is equal to thediameter of the cylindrical core drill section.

The cylindrical exterior surface of the core drill section acts as guidemeans to ensure the circularity of the drilled hole, for as thescrewdriver turns the core drill section into the wall material, the bitteeth T₁ and T₂ proceed to cut a round hole whose form is defined by thecylindrical exterior surface.

After the drill section has drilled a hole in the wall W, as the anchorcontinues to be turned by the screwdriver, the shank section of theanchor then enters this hole, and the threading of this section taps thedrilled hole, until, as shown in FIG. 14, the head of the shank sectionengages the surface of the wall.

The length of the self-drilling anchor is determined by the thickness ofthe hollow wall for which it is intended; for when the anchor is beinginstalled, its drill section 31, for most materials, should project fromthe rear of the wall before the threads of the shank section engage andtap the drilled hole. In FIG. 14, the length of the shank section 25 islonger than the thickness of the wall; hence a lower portion of theshank section sticks out of the wall.

To hold a fixture 33 against the outer surface of wall W, a threadedfastener 34 is inserted through the mounting hole in the fixture intothe bore of the shank section and is screwed therein, the fastenertapping its way into the bore. The length of fastener 34 is greater thanthat of the anchor; hence as it turns and advances, it goes through thebore of the shank section and then through the bore of the cylindricalcore drill section, the screw then emerging from the drill section, asshown in FIG. 14.

In this self-drilling anchor, other than the core of pulverized wallmaterial disposed within the bore of the core drill section, there isnothing to impede passage of the fastener, and as the fastener advancesbeyond the shank section, it ejects the core of pulverized material fromthe drill section, which is neither deflected nor split to permit suchpassage. Hence the integrity of the anchor is maintained, and should itbe later desirable to unscrew the anchor from the wall, this can be donewithout difficulty, thereby making it possible to again use the anchor.

While there have been shown and described preferred embodiments of animproved self-drilling anchor in accordance with the invention, it willbe appreciated that many changes and modifications may be made thereinwithout, however, departing from the essential spirit thereof. Thusinstead of the bit of the core drill section being formed by a pair ofopposed teeth, the bit may be formed by a circular array of teeth.

I claim:
 1. A self-drilling anchor installable in a hollow wall by meansof a torque producing tool which turns the anchor into the wall incombination with a fastener to hold an object against the wall, saidanchor comprising:A. an externally threaded shank engageable by thetool; and B. cutting means extending axially from the shank to cut ahole in the wall as the anchor is being turned by the tool, said cuttingmeans including a cutting member to create a hole in the wall having acircular bank, and a guide element in registration with the cuttingmember adapted to concurrently engage and conform to the bank of thehole as the wall is being cut by the cutting member to ensure thecircularity of the bank whereby the shank as the anchor continues toturn enters and taps a matching thread in the circular bank and isthereby securely held in the wall, said shank having a longitudinal borefor receiving and engaging said fastener to hold an object adjacent thewall, said cutting means having a through passage therein communicatingwith the bore to permit the fastener to advance into and beyond thecutting means.
 2. An anchor as set forth in claim 1, having an enlargedhead at the upper end of the shank to receive said tool.
 3. An anchor asset forth in claim 1, formed of synthetic plastic material.
 4. An anchoras set forth in claim 1, formed of nylon.
 5. An anchor as set forth inclaim 1, formed of corrosion-resistant metal.
 6. An anchor as set forthin claim 1, in which the drilling means if formed by a core drill havingan arcuate outer wall that constitutes said guide element.